1. DeviceNet
2400, 2500, 26/2700

2. This Talk DeviceNet - Background DeviceNet v. Profibus DP
Operation of 26/2700
Operation of 2400 and 2500

3. DeviceNet Based on CAN (Controller Area Network)
CAN provides deterministic “peer-to-peer” networking
DeviceNet is to CAN as Modbus is to RS485
Higher Level Protocol designed for Industrial applications
Power available on the same cabling (up to 8 amps at 24VDC)
Designed by Allen Bradley as proprietary fieldbus for linking simple devices (e.g. limit switches) to a central PLC
Now fully “open” and owned by ODVA (Open DeviceNet Vendors Association)

4. DeviceNet Usually uses a PLC “Master” and “Slave” devices
Typically very simple networks (< 600 bytes of Input and Output for the whole network).
Limited data capacity, imposed by slow maximum speed (500K), and CAN limitations
Limited physical network length (discussed later)
DeviceNet can support complex peer-to-peer networks and
more complex devices. However in practice, this is almost
never done.

5. I/O Data Transfer Model
Slave Input Data (To PLC)
PLC Registers
Temperature
Working Setpoint
Loop Output Power
Alarm Status word
Slave Output Data (From PLC)
Target Setpoint
Manual Output
Application uses
data from input
registers and
sets values in
output registers
Scanner transfers I/O
Data from/to PLC once
each scan cycle for each
slave ~ 10mS cycle

6. I/O Transfer Methods
“Polled” I/O
Master requests Input values from slave and sends Outputs on each bus cycle
“Cyclic” I/O
Slave sends data at predefined time intervals
Change of State (“COS”)
Slave sends data only when a change of value has been detected.
Bit Strobe
A very efficient way of requesting a small amount of data (less than 4 16 bit words) from a slave device.
Most often used method is Polled I/O - others useful to
increase throughput

7. DeviceNet “Objects” DeviceNet devices made up of a set of “Objects”
Really just a way of organising parameters by functions
Values are addressed over comms by:
“Class” - a number defining the type of object from a predefined list (e.g. Class 1 is a “DeviceNet identity” object holding information on Device model and manufacturer.)
“Instance” - If more than one object of a given class exists, this number identifies a particular instance.
“Attribute” - a number between 0 and 199 defining the parameter within the object.
Objects accessed using “explicit messaging”.

8. Explicit Messaging
Like Modbus, i.e. a single shot read or write request.
Read or write an object by class/instance/attribute.
Typically used by Configuration Tool to configure or commission a slave device
Can also be used by a PLC master to access infrequently used variables in a slave
Used in 2600 and 2700 to write program data

9. “EDS” files and Commissioning
A bit like Profibus GSD files - define device capabilities
However No “GSD file editor” equivalent in DeviceNet - Eurotherm slaves configured using standard DeviceNet tools.

10. DeviceNet v. Profibus DeviceNet Profibus DP Max Speed 12 Mbaud
Max speed 500 kbaud
125 kbaud
250 kbaud
500 kbaud
Max Nodes 64 per network
Power supplied by network
Complex and extendable architecture
Flexible trunk/drop topology
Self Declaration of Nodes
Profibus DP
Max Speed 12 Mbaud
500 kbaud
1.5 mbaud
12 mbaud
Max Nodes 32 per segment, 128 per network (with repeaters.
No Power on network
Simple, fixed architecture
Trunk only topology
Fixed network configuration
Profibus DP is generally simpler to use and more capable. The only real practical advantage to DeviceNet is when linking into Allen Bradley/Omron systems

11. 2600/2700 on DeviceNet
Fully Configurable I/O Messaging
0 to 60 “Input” variables (from PLC)
0 to 60 “Outputs” (sent to PLC)
Polled/Cyclic/COS/Bit Strobe available
Configured via an ‘Assembly Configuration Object” using standard Rockwell tools
Support for 32 bit (IEEE floats and long integers)
“Application” Object
Allows explicit messaging access to 200 frequently used variables
Includes 32 configurable ‘attributes’ assignable to any instrument parameter
“Tag Access” object
Permits Modbus style ‘block’ read and writes.
Used for program download and access to infrequently used variables.
Currently under Beta test for release around April

12. 2400 on DeviceNet Same as 26/2700, except:
Only 10 configurable parameters in “Application Object”
No support for IEEE numbers
Available for beta test: release scheduled for May/June.

13. 2500 on DeviceNet
As 2600/2700 except ALL 200 parameters in the application object are configurable
Beta test units available: release scheduled for April/May

14. Some closing remarks
With the release of the new DeviceNet interface, Eurotherm will have a very complete and scalable DeviceNet offering, from 2200 up through 2700.
Should be possible to repeat success of Profibus with DeviceNet
Consider targeting Allen Bradley and Omron OEMs
Consider what further training you would like!